OpenCV： imshow后不加waitkey无法显示视频

cvWaitKey(x) / cv::waitKey(x) does two things:

1. It waits for x milliseconds for a key press. If a key was pressed during that time, it returns the key‘s ASCII code. Otherwise, it returns -1.
2. It handles any windowing events, such as creating windows with cv::namedWindow(), or showing images with cv::imshow().

A common mistake for opencv newcomers is to call cv::imshow() in a loop through video frames, without following up each draw with cv::waitKey(30). In this case, nothing appears on screen, because highgui is never given time to process the draw requests from cv::imshow().

所以imshow之后还是加上waitkey语句吧，为节约时间就设置为最小值1好了。

cv::waitkey(1);